Listeria and listeriosis in the milk production's chain: An up-to-date [Listeria e listeriosi nella filiera latte: breve rassegna critica]

Listeriosis is a severe infectious disease which affects humans as well as animals; in most cases the disease is caused by Listeria monocytogenes, but in some cases the same clinical features can also be induced by other Listeriae such as L. ivanovii and L. innocua. L. monocytogenes and the other Listeriae are widely distributed in nature because their intrinsic resistance to the environmental stresses. They can be found on vegetables, water and soil, as well as in feces of domestic and wild animals and in the close environment of animals. The main reservoirs of Listeria spp. are the ruminants, but in literature there are very few references about the percentage of healthy carriers of Listeria among cattle, sheep and goat. Listeria spp. may be recovered from a variety of animals and environments, and silages may be a good source of these pathogens to ruminants. So the ruminants may be a vehicle of transmission of virulent Listeria strains to humans, by means of raw milk and dairy products which can contain Listeria. In lactating cows, sheep and goats Listeria spp. may also cause a specific mastitis, but the role of this form of mastitis remains unclear in the diffusion of Listeriae to raw bulk milk. In animals the listeriosis often becomes invasive, resulting in severe clinical outcomes such as encephalitis, meningitis, septicaemia and spontaneous abortion during the last trimester of pregnancy. In humans the listeriosis is for the 99% a foodborne disease and the infection is a serious threat to vulnerable individuals, such as pregnant women, the elderly, newborns and immunocompromised patients. Dairy products are an important source of this pathogen. In fact L. monocytogenes has been isolated from a large variety of raw and processed dairy products foods, including raw and pasteurized milk. This brief review aims to give an up-to-date of the distribution of Listeriae and listeriosis among livestock (specially ruminants) as well along the milk production chain, emphasizing the role of raw milk and dairy products in the epidemiology of human listeriosis.